It is known that reduced coenzyme Q10 can be obtained, for example, by a method comprising producing coenzyme Q10 by a conventionally known method such as synthesis, fermentation, extraction from a naturally occurring substance and the like, and concentrating a reduced coenzyme Q10 fraction in an eluate from chromatography and the like (see JP-A-10-109933). In this case, oxidized coenzyme Q10 contained in the above-mentioned reduced coenzyme Q10 can be reduced with a general reducing agent such as sodium borohydride, sodium dithionite (sodium hydrosulfite) and the like, and concentrated by chromatography, and that the reduced coenzyme Q10 can also be obtained by a method comprising reacting existing highly pure coenzyme Q10 with the above-mentioned reducing agent.
In addition, production methods for conveniently obtaining reduced coenzyme Q10 are also disclosed (e.g., WO 03/06408, WO 03/06409 and WO 03/32967).
However, reduced coenzyme Q10 is easily oxidized by molecular oxygen into oxidized coenzyme Q10, and therefore, stabilization of reduced coenzyme Q10 is an important issue when it is processed into a food, food with nutrient function claims, food for specified health use, nutritional product, nutritional supplement, animal drug, drink, feed, pet food, cosmetic, pharmaceutical product, therapeutic drug, prophylactic drug and the like, or a material or composition therefor, or preserved after processing and the like. Complete removal or blocking of oxygen during the above-mentioned processing and preservation is extremely difficult, and remaining or admixed oxygen particularly during heating for processing and long-term preservation exerts a markedly adverse effect. The above-mentioned oxidation is directly related to quality problems such as the by-product oxidized coenzyme Q10.
As mentioned above, stabilization of reduced coenzyme Q10 (protection of oxidation) is a highly important object. However, since reduced coenzyme Q10 is not commercially available to date, the study of methods and compositions for stable retention of reduced coenzyme Q10 has not been undertaken very much.
As a conventionally-known method for stably retaining reduced coenzyme Q10, a method including addition of a reducing agent is known. However, some of the reducing agents used therefor are not suitable for food and pharmaceutical agents. For example, WO 01/52822, which discloses a composition concurrently containing a reducing agent and a production method thereof, also discloses (1) a composition comprising reduced coenzyme Q10; a reducing agent in an amount effective for eliminating oxidation of reduced coenzyme Q10 into oxidized coenzyme Q10; a surfactant, vegetable oil or a mixture thereof in an amount effective for dissolving the above-mentioned reduced coenzyme Q10 and the above-mentioned reducing agent; and a solvent as necessary, (2) a composition for oral administration wherein the above-mentioned composition is prepared into a gelatin capsule or a tablet, and (3) a method of preparing the above-mentioned composition containing reduced coenzyme Q10 in situ using oxidized coenzyme Q10 and a reducing agent. However, no detailed description relating to the quality, stabilizing effect and the like of the reduced coenzyme Q10 contained in the composition is provided, and the expected level of stabilization is not clear.
In addition, the above-mentioned composition and preparation method thereof are highly complicated and complex since plural roles are conferred to the composition (i.e., firstly, a role as a reaction site for reducing oxidized coenzyme Q10 to reduced coenzyme Q10, and secondly, a role of stably retaining reduced coenzyme Q10). Moreover, the above-mentioned composition and a preparation method thereof are not entirely safe because the reaction mixture is used as it is. In other words, ascorbic acids to be used as reducing agents are oxidized to produce a considerable amount of dehydroascorbic acids, and the dehydroascorbic acids get mixed in with the above-mentioned composition, posing a problem. Dehydroascorbic acids and oxalic acid produced by decomposition from dehydroascorbic acids are highly noxious, unlike ascorbic acids. For example, an increased amount of lipid peroxide and a decreased amount of antioxidants in the liver and kidney, and an increased amount of oxalic acid in the kidney have been reported, and side effects such as decreased resistance to oxidation stress, easy onset of ureteral lithiasis (Nutrition Research Vol. 13, page 667-676, 1993) and the like are feared.